This invention relates to a puffer or piston type fluid blast circuit interrupter in which a piston structure provides a desirable fluid blasting action during contact separation with the fluid flow passing over the arc to effect its extinction. Cromer et al, U.S. Pat. No. 3,095,490 teaches generally a fluid blast circuit interrupter of a type in which the separation in the contact structure is deliberately delayed until a predetermined pressure buildup occurs. Frink et al, U.S. Pat. No. 3,588,407 teaches a gas blast circuit interrupter of the puffer type where gas is vented in parallel paths but where both parallel paths are internal to a pair of hollow conductors. Saffold et al, U.S. Pat. No. 3,555,225 teaches a gas blast circuit interrupter similar to that which is taught in the previously described Frink et al patent but where the insulating nozzle is always relatively stationary. Baker, U.S. Pat. No. 2,933,575 teaches a circuit interrupter of the gas blast type where the nozzle or the insulating portion may move not only relative to the separable contacts but also relative to other fixed portions of the circuit breaker which in turn are fixedly attached to at least one of the separable contacts. It would be advantageous to provide a circuit interrupter of the gas blast puffer piston type wherein a hollow electrical contact and an electrically insulating puffer nozzle are provided in fixed relationship with each other for engagement with a relatively solid electrical conductor and where compressed insulating arc-extinguishing gas is provided between the annular conductor and the solid conductor during an interrupting operation. It would be further advantageous if the gas was provided with dual or parallel paths for venting into ambient pressure regions of the circuit interrupter after the interruption operation has begun. It would be further advantageous to provide one of these latter parallel paths for gas venting through the annular conductor and the other parallel path for gas venting around the outer surface of the solid conductor rather than through it.